diff --git a/commands/trekreview.md b/commands/trekreview.md
index 288072d..a7f593c 100644
--- a/commands/trekreview.md
+++ b/commands/trekreview.md
@@ -52,6 +52,7 @@ FLAG_SCHEMA `trekreview` entry):
 | `--validate` | boolean | Schema-only check on existing `{project_dir}/review.md`. No LLM calls. |
 | `--dry-run` | boolean | Print the discovered scope and triage map. Skip writes. |
 | `--fg` | boolean | No-op alias (foreground is default). |
+| `--workflow` | boolean | **(opt-in, NW2)** Run Phase 5–6 on the bake-off-validated Workflow substrate (`scripts/trekreview-armB.workflow.mjs`) instead of the default prose Agent-tool path. Requires **Claude Code 2.1.154+**. Combines with `--quick`. See *§ Phase 5–6 via the Workflow substrate*. |
 
 Resolution:
 1. If `--project` is missing, print usage and stop:
@@ -75,6 +76,13 @@ Set `mode`:
 - `quick` if `--quick` is set.
 - `default` otherwise.
 
+Set `workflow_substrate` (orthogonal to `mode` — a substrate choice, not a behavior mode):
+- `true` if `--workflow` is set — Phase 5–6 run on the Workflow substrate (see the Phase 5
+  routing gate). The Workflow tool requires **Claude Code 2.1.154+**; if it is unavailable,
+  fall back to the prose path and note the fallback in the Executive Summary.
+- `false` otherwise. **Default stays prose**: the substrate is opt-in, so the lower
+  portability floor of the prose path is preserved unless the operator opts in.
+
 ## Phase 2 — Validate brief
 
 Run the brief validator in soft mode — the brief is upstream context, not
@@ -181,6 +189,12 @@ If `mode == dry-run`: print the triage map and exit.
 
 ## Phase 5 — Launch parallel reviewers
 
+**Substrate routing (opt-in `--workflow`).** When `workflow_substrate == true`, run
+Phases 5–6 via the Workflow substrate documented in *§ Phase 5–6 via the Workflow
+substrate* (below Phase 6), then resume at Phase 7 with the returned
+`{verdict, findings}`. When `false` (the default), run the prose Agent-tool path
+described in the rest of this phase.
+
 Launch two reviewer agents **in parallel** via the Agent tool — one
 message, multiple tool calls.
 
@@ -240,6 +254,54 @@ The coordinator's output is the full review.md content — frontmatter +
 body sections + trailing JSON block. Do NOT re-run the reviewers based
 on the coordinator's output.
 
+## Phase 5–6 via the Workflow substrate (opt-in `--workflow`)
+
+Runs **only** when `workflow_substrate == true`. This is the **NW2 port**: it expresses
+the SAME Phase 5–6 pipeline (parallel reviewers → triplet-dedup → coordinator verdict) as
+a single Workflow, reusing the NW1 findings schema. The S10 bake-off found it
+**fidelity-equivalent** to the prose path — see `docs/T2-bakeoff-results.md` (verdict
+**POSITIVE**: verdict-match 1.0, issue-coverage 100%, `(file,rule_key)` jaccard ≥
+within-arm, tokens +4.4%). It stays **opt-in**, not the default, because the Workflow tool
+raises the consumer floor to **Claude Code 2.1.154+** (outward-facing; the prose path
+keeps the lower floor).
+
+Invoke the port via the **Workflow** tool with the Phase 1–4 output pinned into `args`:
+
+```
+Workflow({
+  scriptPath: "${CLAUDE_PLUGIN_ROOT}/scripts/trekreview-armB.workflow.mjs",
+  args: {
+    briefPath: "{brief_path}",
+    diffPath:  "{path to the unified diff file from Phase 3}",
+    triage:    "{triage map as 'path → treatment' lines from Phase 4}",
+    quick:     {true if mode == quick, else false}
+  }
+})
+```
+
+Contract (verified in S10 part B — follow exactly):
+- **Pass `args` as a JSON object.** The script defensively re-parses a JSON *string*, but
+  the object form is the contract.
+- **Reviewers are `StructuredOutput`-schema-forced** — `rule_key` is enum-enforced at the
+  tool layer (stronger than the prose path's post-hoc NW1 check), so there is no
+  `JSON.parse`/re-ask dance.
+- **Recover the result from the `RESULT_JSON:{…}` line** inside the workflow output logs.
+  The script returns `{verdict, findings, ...}` AND logs it as that line; the
+  notification's `<result>` may be truncated, so parse the logged line.
+- The reviewer/coordinator agentTypes are namespaced inside the script
+  (`voyage:brief-conformance-reviewer`, `voyage:code-correctness-reviewer`,
+  `voyage:review-coordinator`).
+
+Then continue at **Phase 7** exactly as the prose path does — Phase 7 rendering, Phase 8
+validation, and the operator gate are **shared** and substrate-independent (both paths
+return the same `{verdict, findings}` shape).
+
+**Known limitation (per bake-off §Posture, surfaced not hidden).** Classifier interference
+was measured **0** at 9-agent concurrency in the session's default permission mode; an
+explicit `auto`/`bypass`-mode re-run was not performed (the permission mode is operator-set,
+not settable from within a session). trekreview's small fan-out showed 0 interference in S8
+and S10. The large fan-out case (the trekplan swarm) is out of NW2 scope.
+
 ## Phase 7 — Write review.md
 
 Write the coordinator's output verbatim to:
diff --git a/docs/command-modes.md b/docs/command-modes.md
index f9e3256..2ff0c7e 100644
--- a/docs/command-modes.md
+++ b/docs/command-modes.md
@@ -72,6 +72,7 @@ If `{project_dir}/architecture/overview.md` exists (typically produced by an opt
 | `--validate` | Schema-only check on existing `{dir}/review.md`. No LLM calls |
 | `--dry-run` | Print discovered scope + triage map; skip writes |
 | `--fg` | No-op alias (foreground is default) |
+| `--workflow` | (opt-in, NW2) Run Phase 5–6 on the bake-off-validated Workflow substrate (`scripts/trekreview-armB.workflow.mjs`) instead of the default prose path. Default stays prose; requires **Claude Code 2.1.154+** (raises the consumer floor — opt-in for portability). Fidelity-equivalent per `docs/T2-bakeoff-results.md` |
 | `--profile <name>` | (v4.1.0) Model profile for the review phase. |
 
 ## /trekcontinue modes
diff --git a/lib/parsers/arg-parser.mjs b/lib/parsers/arg-parser.mjs
index c843eb1..ab27e55 100644
--- a/lib/parsers/arg-parser.mjs
+++ b/lib/parsers/arg-parser.mjs
@@ -27,7 +27,7 @@ const FLAG_SCHEMA = {
     aliases: {},
   },
   trekreview: {
-    boolean: ['--quick', '--fg', '--dry-run', '--validate'],
+    boolean: ['--quick', '--fg', '--dry-run', '--validate', '--workflow'],
     valued: ['--project', '--since', '--profile'],
     aliases: {},
   },
diff --git a/tests/commands/trekreview.test.mjs b/tests/commands/trekreview.test.mjs
index e66ef00..bf00ab6 100644
--- a/tests/commands/trekreview.test.mjs
+++ b/tests/commands/trekreview.test.mjs
@@ -13,9 +13,11 @@ import { parseDocument } from '../../lib/util/frontmatter.mjs';
 const HERE = dirname(fileURLToPath(import.meta.url));
 const ROOT = join(HERE, '..', '..');
 const COMMAND_FILE = join(ROOT, 'commands', 'trekreview.md');
+const MODES_DOC = join(ROOT, 'docs', 'command-modes.md');
 const PHASE = 'review';
 
 function read() { return readFileSync(COMMAND_FILE, 'utf8'); }
+function readModes() { return readFileSync(MODES_DOC, 'utf8'); }
 function readFixture(name) { return readFileSync(join(ROOT, 'tests', 'fixtures', name), 'utf8'); }
 function frontmatterOf(text) {
   const doc = parseDocument(text);
@@ -72,3 +74,50 @@ test('trekreview — SC7: brief_version 2.1 + no phase_signals + no partial →
     `sequencing gate must fire; errors=${JSON.stringify(r.errors)}`,
   );
 });
+
+// --- S11 (NW2 part B) — opt-in --workflow substrate routing ---
+
+test('trekreview — Phase 1 flag table documents the --workflow opt-in flag', () => {
+  const text = read();
+  assert.match(text, /--workflow/,
+    'commands/trekreview.md must document the --workflow opt-in flag (NW2 part B)');
+});
+
+test('trekreview — --workflow routes Phase 5–6 to the validated NW2 Workflow port script', () => {
+  const text = read();
+  assert.ok(text.includes('scripts/trekreview-armB.workflow.mjs'),
+    'the --workflow route must reference the bake-off-validated NW2 Workflow port script');
+});
+
+test('trekreview — Workflow path is opt-in; default stays prose (portability floor)', () => {
+  const text = read();
+  assert.match(text, /opt-in/i, '--workflow must be described as opt-in');
+  assert.ok(text.includes('Default stays prose'),
+    'the command must state the default Phase 5–6 path stays prose (not Workflow)');
+});
+
+test('trekreview — Workflow opt-in documents the Claude Code 2.1.154+ floor', () => {
+  const text = read();
+  assert.match(text, /2\.1\.154/,
+    'the --workflow path raises the consumer floor and must document Claude Code 2.1.154+');
+});
+
+test('trekreview — bake-off evidence (fidelity-equivalent / T2 results) is cited for the opt-in', () => {
+  const text = read();
+  assert.ok(
+    text.includes('T2-bakeoff-results.md') && /fidelity-equivalent/i.test(text),
+    'the opt-in must cite the S10 bake-off (docs/T2-bakeoff-results.md) fidelity-equivalence verdict',
+  );
+});
+
+test('command-modes.md — /trekreview table documents --workflow + its CC floor', () => {
+  const text = readModes();
+  const start = text.indexOf('## /trekreview modes');
+  assert.ok(start >= 0, 'command-modes.md missing "## /trekreview modes" section');
+  const end = text.indexOf('\n## ', start + 1);
+  const section = text.slice(start, end === -1 ? undefined : end);
+  assert.match(section, /--workflow/,
+    'command-modes.md /trekreview table must list the --workflow opt-in flag');
+  assert.match(section, /2\.1\.154/,
+    'command-modes.md /trekreview --workflow row must note the Claude Code 2.1.154+ floor');
+});
diff --git a/tests/lib/arg-parser.test.mjs b/tests/lib/arg-parser.test.mjs
index 0a04956..f59c0b8 100644
--- a/tests/lib/arg-parser.test.mjs
+++ b/tests/lib/arg-parser.test.mjs
@@ -97,6 +97,23 @@ test('trekreview — unknown flag goes to unknown[]', () => {
   assert.ok(r.unknown.includes('--mystery'));
 });
 
+// --- S11 (NW2 part B) — opt-in --workflow substrate flag ---
+
+test('trekreview — --workflow boolean flag (NW2 opt-in substrate)', () => {
+  const r = parseArgs('--workflow', 'trekreview');
+  assert.equal(r.flags['--workflow'], true);
+  assert.ok(!r.unknown.includes('--workflow'),
+    '--workflow must be a recognized trekreview flag, not unknown[]');
+});
+
+test('trekreview — --workflow combines with --quick + --project', () => {
+  const r = parseArgs('--workflow --quick --project .claude/projects/x', 'trekreview');
+  assert.equal(r.flags['--workflow'], true);
+  assert.equal(r.flags['--quick'], true);
+  assert.equal(r.flags['--project'], '.claude/projects/x');
+  assert.deepEqual(r.unknown, []);
+});
+
 test('trekcontinue — empty args produce no flags and no positional', () => {
   const r = parseArgs('', 'trekcontinue');
   assert.equal(r.command, 'trekcontinue');